St. Petersburg authorities had prohibited the march, only granting permission for a rally far from the city center, but the activists defied the ban and marched down the Nevsky Prospekt , the city's main street, blocking traffic. The mayor called the protesters extremists trying to destabilize the city ahead of local elections.
Riot police beat dozens of protesters with truncheons, but several thousand broke through police cordons. They marched toward the city center and rallied for about 40 minutes until police moved in again, detaining people, and dragging them into buses.
Several activists attacked a law enforcement officer. Between 20 and 30 people were detained, the ITAR-Tass news agency reported.
Garry Kasparov , former world chess champion who helped organize the event, said on Ekho Moskvy radio that the participants numbered as many as 6,000, though the crowd appeared to be about half that number. Among those detained were the head of the radical National Bolshevik Party and an independent city legislator.
"The authorities are destroying . . . the constitutional structure, rights, and freedoms," former prime minister Mikhail Kasyanov , who now heads an opposition movement, told AP Television News.
The activists accused Putin's government of stifling freedom of speech, and damaging democratic institutions by abolishing direct elections of provincial governors and creating an obedient parliament.
The sidelined and often divided opposition has faced increased harassment in recent years, with protest meetings barred on suspicious legal grounds, or party congresses broken up or canceled for no reason. Putin's policies have drawn criticism from the United States, straining ties between the two countries.
In December, police pulled hundreds of opposition activists off buses and trains and detained them ahead of an anti government demonstration in Moscow. The next month, police arrested dozens of Bolshevik party members rallying in support of activists detained in earlier unauthorized protests.
